The closest known prior art is that found in U.S. Pat. No. 3,581,227 which issued May 25, 1971 to Theodore J. Podgorski for an "Adjustable, Thin Membrane Mirror For Use In The Stabilization Of Ring Lasers." The patent shows a triangular ring laser path with mirrors at each of the corners of the triangle. One of the corners has a mirror whose in-out position is controlled in response to an electrical signal. The position may be controlled, typically, to tune the laser or to minimize lock-in between two laser frequencies.
The structure shown and claimed uses a block of the same dimensionally stable material as that used for the laser housing. The block is circularly grooved on its internal side to leave a depressed thin integral gas-impervious annular web surrounding a light-reflecting surface. The light-reflecting surface is positioned internally in the web on a circularly cylindrical central post which was left inwardly-standing from an integral with the membrane for that purpose. Radially outward from the groove is a rigid annular member which is integral with the membrane but which extends axially external to the region enclosed by the membrane. Within an opening formed by the rigid annular member but external to the membrane is a stack of piezoelectric ceramic wafers which bear against the external side of the membrane and of the inwardly-standing post. The opening containing the ceramic wafer stack is closed with a rigid disc-like member which is rigidly attached to the annular member to support the stack of ceramic wafers.
When an electrical signal is applied to the wafer stack, the stack produces a force between the supporting rigid disc-like member and the external end of the inwardly-standing post and mirror. The force from the ceramic stack is principally axial, but it also may have a twisting force which tilts the inwardly-extending post and mirror. Such tilting reduces the utility of the mirror.